Enhancing the performance of tin-based perovskite solar cells through solvent purification of tin iodide

Abstract

Tin (Sn)-based perovskites are very promising for the fabrication of low-toxicity lead-free perovskite solar cells (PSCs), but they suffer from easy oxidation of Sn²⁺ to Sn⁴⁺ which leads to poor performance. Herein, we report a facile solution method for the purification of SnI₂ in Sn-based PSCs by toluene washing. We found that toluene can dissolve undesired SnI₄ and retain the SnI₂ source, which enabled us to fabricate efficient Sn-based PSCs with much-reduced harmful Sn⁴⁺ impurities. The as-prepared formamidinium tin iodide perovskite films have markedly improved film morphology, enhanced crystalline quality, increased carrier lifetime, etc. Ultimately, the best-performing solar cell obtained using toluene-purified SnI₂ precursors delivers a promising power conversion efficiency of 10.70% and the efficiency even increases to 11.06% after nearly one month of storage in an N₂ atmosphere. This work paves a facile way for overcoming the complicated purification of SnI₂ for efficient Sn-based PSCs.